Electric discharge tube and process of operating same



Aug. 28, 1934. ZECHER 1,971,891

ELECTRIC DISCHARGE TUBE AND PROCESS OF OPERATING SAME Filed May 22. 1930In ved'or,

A ctc' r/ze y- Patented Aug. 28, 1934 UNITED STATES ELECTRIC DISCHARGETUBE AND PROCESS OF OPERATING SADIE Gustav Zecher, Eindhoven,Netherlands, assignor, by mesne assignments, to GeneralElectric Company,a corporation of New York Application May 22, 1990, Serial No. 454,606In the Netherlands June 8, 1929 12 Claims. (o1. 176-42) This inventionrelates to an electrical discharge tube, used either as an illuminatingelement, or as a generator of special properties radiation, such asultra-violet rays. For such purposes the tube contains electrodematerial consisting of an alloy or mixture of metals in the form of anamalgam, say cadmium amalgam. In this way it is possible to obtain lightor other radiation from the tube showing the characteristic spectrum ofa metal found in the amalgam without danger of cracking the tube whenits liquid electrodes solidify, whereas, if such metal, say cadmium, orsodium, is used by itself as electrode material there is risk that thetube will break either when the metal cools to a solid or when the tubeis again started.

If a suitable alloy or mixture of metals is made the basis for theintroduction of any metal whose spectrum is desired, it is found thatthe danger of destroying the tube is greatly lessened compared to therisks run when that particular metal is used as a sole electrodematerial. Discharge tubes of the kind in question, however, whenoperated with electrodes consisting of a mixture or alloy of metalspresent the disadvantage that the light or radiation from the dischargeexhibits essentially the spectrum of the most volatile metal in themixture, consequently, if an amalgram is used, the spectrum would beessentially that of mercury. For this reason it has been found necessaryto connect a condensing chamber to the discharge tube of such a size asto be just capable of storing all the vapor of the most volatile metalof the alloy, the mercury, for

instance, in case an alloy is used as electrode material.

For some time after such a discharge tube, to which a condensing chamberor vesselis connected, is put into service the discharge will take placeessentially through the vapor of the least volatile metal, hence thelight given ofi will exhibit essentially the spectrum of the vapor ofsaid metal. After the discharge has been interrupted the metal which hascollected in the condensing chamber must be again mixed with the lessvolatile metal, which may be effected by tipping the discharge tube,otherwise the tube might crack. It has been found, however, that asuflicient admixture does not take place in every case so that incertain instances a breakage of the tube may result. Accordingly whenusing such discharge tubes care must be taken that when the discharge isinterrupted the metal collected in the condens- 7 done automatically butthe necessary devices materially complicate the apparatus.

As one feature of this invention it has been discovered that tubes ofthe kind described can be operated safely and continuously without acondensing chamber connected to the discharge tube, that is, it ispossible to suppress the separate condensing vessel heretofore connectedto the discharge tube, and it is one of the objects of the invention todo so.

According to the invention the discharge tube used therein preferablycontains an alloy or mixture of metals constituting an electrode of thetube. This alloy or mixture may consist for example of an amalgam, saycadmium amalgam. Furthermore the structure of the tube is so de signedas to present a discharge space through which passes a separate channelserving to constantly return the metal condensed in the operation of thetube, say mercury, to the space that contains the electrode alloy ormixture of metals. In this way it is possible to obtain a light spec--trum from the discharge tube which is essentially that of the leastvolatile metal, and this is a further object of the invention. Theparticular structure of the tube will be described in detail below.

In the drawing which is to be considered as part of this specification:Fig. 1 is a diagrammatic illustration of a discharge tube, exhibitingone form of my invention as described in this specification. Figs. 2 and3 show diagrams of modifications of the invention.

Referring to Figure 1, the discharge tube 1 is shaped as a reversed, Utube. The limb 2 contains an alloy or mixture of metals 3 which mayconsist of an amalgam, say cadmium amalgam,'or of an alloy of bismuthand mercury. Good results have, for example, been obtained with acadmium amalgam containing 20% of cadmium. The alloy 3 constitutes anelectrode of the discharge tube and is connected to a leading-in wire-4,taken through the wall of the tube. The limb 5 of the discharge tubecontains an electrode which consists, for example, of a supply ofmercury 6 connected to the leading-in wire '7. Obviously this electrodemay consist of a solid substance, or of the same alloy as the electrode3, and it may be preferable for the ends of the'tube to be sphericallyenlarged. A short distance above the electrode 6 a small tube 8 issealed into limb 5 and opens out just above the electrode 6. This tube 8has a bent, or zigzag, shape and has its other end sealed to the lowerend of limb 2.

' discharge;

Discharge tubes of the kind illustrated will not run on the usualoperating voltage until they have been ignited. This is accomplished invarious ways, well known in the art, for instance the tube may be tiltedor inclined to bring about an instantaneous contact between the metalsof the running electrodes, and in this connection it is necessary toprovide that the opening of tube 8 above electrode 6 should be solocated and of such a character that no electrode material can flow intotube 8. Another way to effect preliminary ignition is to temporarilyapply a very high voltage, and in some cases amalgam 3 is heated.

Supposing the tube to be successfully started by one of the well knownmethods referred to, with amalgam 3 as anode and electrode '7 ascathode, the first effect will be to primarily volatilize the mercurycontained in amalgam 3. Consequently, in addition to the spectrum of thecadmium, supposing a cadmium amalgam, the light generated will show manymercury lines. The mercury volatilized condenses in the upper part oflimb 5, thusincreasing the quantity of mercury in that limb. When themeniscus of electrode 6 reaches the opening of tube 8 the condensedmercury will be led back through the said tube to the lower part of limb2. It has been found after the tube has been running for some time thesurface of electrode3 substantially becomes cadmium and that thedischarge takes place essentially in a vapor of cadmium of highpressure. The light generated by this discharge contains manyultra-violet rays, which will pass freely through the wall of the tubeif thesaid wall is of quartz or other transparent material for suchrays. Thus the tube can be used as a generator of ultra-violet rays, andserve as an artificial sunlight, or a source of radiation forsterilization purposes.

It has been found that with continued operation of the tube the quantityof mercury which volatilizes is but slight and does not effect thespectrum of the light emitted to any extent. Furthermore the device verygreatly reduces the risk of breakage on starting or stopping the tubefor the constant return or circulation of the condensed mercury keepsthe average percentage of metals forming the amalgam electrode 3 nearlyconstant.

The discharge tube shown in Figure 2 has a straight cylindrical part 9,the spherically enlarged end of which contains an alloy or mixture ofmetals, say cadmium amalgam or a mixture of mercury, cadmium and bismuth10 electrically connected to leading-in wire 11 The upper part of tube 9has sealed to it, a short distance from the end, a cup. shaped enlargedcylinder 12 into which the end of tube 9 projects, the projection formsa circular-channel, or chute, at the base of cup 12 that connects with atube 18 extending parallel to tube 9 and sealed into the sphericalenlargement ,of said tube 9. Tube 18 as shown is considerably smallerthan tube 9 and extends well below the surface of the electrode 10,which prevents any possibility of the condensed vapor carried by tube'18 congealing, or solidifying when about to discharge into theelectrode 10.

Tube 9 may contain a suitable gaseous filling, for instance, one of therare gases, the presence of which will assist the initial ignition ofthe The enlargement 12 carries a stem sealed therein to support anincandescent cathode 14 of the filament type, which is heated by wires15 and 16 passing through stem 13 and forming one electrode of the tube9. The other electrode 10 is connected to the external circuit by wire11.

The function of tube 18 is to return the condensed vapor of mercury, ormore broadly of the most volatile constituent of the amalgam electrode10. Once the tube has settled into steady running relation there will beonly a slight flow through tube 18 and as explained above it is foundthat in this modification also the cadmium of the amalgam collectsessentially on the surface of the electrode 10, thus giving a dischargethrough tube 9 practically wholly in cadmium vapor with its resultingspectrum in radiation.

The form of the invention shown in Fig. 3 is similar to Fig. 2 in regardto arrangement of the discharge portion of the tube and its provisionsfor circulating condensed vapors back to the electrode pool of amalgam,but all the leadin wires are disposed at one end of the tube which hasadvantages for certain purposes, as sunlight lamps and sometimes inultra-violet ray work.

As shown in Figure 3 lead-in wire 19, running to the electrode at thefar end of the tube passes through the tube which serves also to returnor circulate back the condensed vapors from the top condensing chamberto the lower electrode of amalgam. The wire 19 is protected by a tube 20of insulation material to prevent damage by contact with the vaporflowing in the return tube.

While the channel or tube for returning the condensed vapor to theamalgam pool is shown outside the main discharge tube in the forms ofthe invention illustrated, it will be understood that it might also berun through the discharge space of the tube. The essential feature,broadly, being that the vapor of the most volatile constituents of theamalgamated metals in the electrode is collected by condensation andcaused to fiow through a return conduit to again unite with the body ofthe electrode, and this process or method of operation is continueduntil the discharge settles down to give a spectrum of practically theleast volatile metal vapor. The invention is not to be restricted to anyparticular apparatus or agencies for draining the easily vaporizablemetals of the mixture back to the electrode pool.

What I claim is:

1. An electrical discharge tube containing a mixture of vaporizableelectrode metals having different temperatures of vaporization, adischarge space, a condensation space and a conduit leading from saidcondensation space to the part of the tube containing said mixture ofelectrode metals., and discharging below the surface of said mixture.

2. An electrical discharge tube containing an electrode consisting of amixture of vaporizable metals, one of said metals having a lowervaporization temperature than the others, said tube comprising adischarge space, a condensation space and channel means leading. fromsaid condensation space to the part of the tube containing saidelectrode, and extending below the surface of said electrode.

3. An electrical discharge tube containing an electrode of mercuryamalgamated with a metal having a higher vaporization temperature thanmercury, said tube comprising a discharge space portion, a condensationspace portion and a conduit leading from the condensation space to theportion of the -tube containing said amalgam and opening out below thesurface of the amalgam.

4. An electrical discharge tube shaped substantially as an inverted Utube, an electrode material in one limb of the U tube consisting ofdifferent metals and an electrode in the other limb of a single metal incombination with a conduit connecting the lower portion of said firstnamed electrode with the tube above the second named electrode.

5. A vapor discharge tube comprising an electrode portion containing avaporizable electrode material containing at least two metals, adischarge portion and a condenser portion provided with a cooperatingelectrode and a drain tube adapted to deliver products of condensationbelow the surface of the two-metal electrode.

6. The process of operating electrical discharge tubes which consists inpassing an electrical current through a composite electrode contained inthe tube, decomposing the composite electrode and reuniting itsconstituents below the surface of said electrode during operation of thetube for the purpose of obtaining radiation of given spectrumcharacteristics.

7. A process of operating metal vapour lamps having an arc vesselcontaining electrode means comprising an alloy of metals of differentboiling point and specific gravity, comprising the steps of condensingthe constituent electrode metals after vaporization in the are,collecting the condensate of the light high boiling metal so as to beadjacent to the arc, and collecting the condensate of the heavy lowboiling metals so that it is separated by virtue of its lower specificgravity from the are by a layer of said constituent of said high boilingmetal.

8. A process of operating metal vapour lamps having an arc vesselcontaining electrode means comprising an alloy of metals of differentboiling point and specific gravity, comprising the steps or condensinghigh boiling light constituents of said alloy inside the arc vessel,leading said condensed high boiling constituents directly aftercondensation to the metal at the electrodes, condensing heavy lowerboiling constituents of said alloy outside the arc vessel, collectingsaid condensed low boiling constituents separately from said highboiling constituents, and causing said condensed low boilingconstituents to flow continually back to the metal at the electrodes atthe coldest parts thereof.

9. Metal vapour lamps, comprising the combination of an arc vesselhaving electric pole means and an electrode consisting of an alloy ofmetals of different boiling point and specific gravity, with receivermeans for the low boiling heavy constituents of said alloy, downwardflow conduit means leading from said receiver means, and inlet meanswhereby the low boiling constituent from said conduit means is returnedto said are vessel at a point below the surface of the electrode meansso as to be separated from the are by a layer of high boilingconstituent.

10. A process of operating metal vapor lamps comprising a compositeelectrode which comprises the steps of separating the constituents ofthe composite electrode, leading one of the separated constituents backto the part of the electrode contiguous to the discharge and leading theother of said constituents below the surface of the electrode.

11. An electric discharge device comprising a tubular container,electrodes sealed therein, elec trode leads sealed therein at one endthereof, one of said electrodes being of vaporizable materialand-located at the end of said container opposite that end into whichsaid inleads are sealed, said container having a discharge portion and acondenser portion provided with a cooperating electrode and a drain tubeadapted to deliver products of condensation below the surface of saidvaporizable electrode, the lead for said vaporizable electrode being ledthrough said drain tube.

12. An electric discharge device comprising a tubular container,electrodes sealed therein, electrode leads sealed therein at one endthereof, one of said electrodes being acomposite electrode ofvaporizable material and located at the end of said container oppositethat end into which said inleads are sealed, said container having adischarge portion and a condenser portion provided with a cooperatingthermionic electrode and a drain tube adapted to deliver products ofcondensation below the surface of said vaporizable electrode, the'leadfor said vaporizable electrode being led through said drain tube.

GUSTAV ZECHER.

